Nanoparticles are particles ranging in size from 1 nm to 1 micron in diameter. “Nano” is a prefix which means one billionth (10−9) part of something (Meridian Webster Dictionary). In recent years, the field of nanoparticles has grown due to their unique properties. Many industries utilize nanoparticles, for example the electronics industry, medical science, material science, and environmental science. Noble metal nanoparticles have found widespread use in several technological applications and various wet chemical methods have been reported. See, X. Wang and Y. Li, Chem. Commun., 2007, 2901; Y. Sun and Y. Xia, Science, 2002, 298, 2176; J. Chen, J. M. McLellan, A. Siekkinen, Y. Xiong, Z-Y Li and Y. Xia, J. Am. Chem. Soc., 2006, 128, 14776; J. W. Stone, P. N. Sisco, E. C. Goldsmith, S. C. Baxter and C. J. Murphy, NanoLett., 2007, 7, 116; B. Wiley, Y. Sun and Y. Xia, Acc. Chem. Res., 2007, 40, 1067.
There is great interest in synthesizing metal and semiconductor nanoparticles due to their extraordinary properties, which differ from those of the corresponding bulk material. An example of a nanoparticle is nanoscale zero valent iron (nZVI). Generally, nanoparticles are synthesized in three ways: physically by crushing larger particles, chemically by precipitation, and through gas condensation. Chemical generation is highly varied and can incorporate laser pyrolysis, flame synthesis, combustion, and sol gel approaches. See, U.S. Pat. No. 6,881,490 (Apr. 19, 2005) N. Kambe, Y. D. Blum, B. Chaloner-Gill, S. Chiruvolu, S. Kumar, D. B. MacQueen. Polymer-inorganic particle composites; J. Du, B. Han, Z. Liu and Y. Liu, Cryst. Growth and Design, 2007, 7, 900; B. Wiley, T. Herricks, Y. Sun and Y. Xia, Nano Lett., 2004, 4, 2057; C. J. Murphy, A. M. Gole, S. E. Hunyadi and C. J. Orendorff, Inorg. Chem., 2006, 45, 7544; B. J. Wiley, Y. Chen, J. M. McLellan, Y. Xiong, Z-Y. Li, D. Ginger, and Y. Xia, Nanoletters, 2007, 4, 1032; Y. Xiong, H. Cai, B. J. Wiley, J. Wang, M. J. Kim and Y. Xia, J. Am. Chem. Soc., 2007, 129, 3665; J. Fang, H. You, P. Kong, Y. Yi., X. Song, and B. Ding, Cryst. Growth and Design, 2007, 7, 864; A. Narayan, L. Landstrom and M. Boman, Appl. Surf. Sci., 2003, 137, 208; H. Song, R. M. Rioux, J. D. Hoefelmeyer, R. Komor, K. Niesz, M. Grass, P. Yang and G. A. Somorjai, J. Am. Chem. Soc., 2006, 128, 3027; C. C. Wang, D. H. Chen and T. C. Huang, Colloids Surf., A 2001, 189, 145. Examples of mechanical processes for producing nanoparticles include mechanical attrition (e.g., ball milling), crushing of sponge iron powder, and thermal quenching. Examples of chemical processes for producing nanoparticles include precipitation techniques, sol-gel processes, and inverse-micelle methods. Other chemical or chemically-related processes include gas condensation methods, evaporation techniques, gas anti-solvent recrystallization techniques, precipitation with a compressed fluid anti-solvent, and generation of particles from gas saturated solutions. The commercial significance of nanoparticles is limited by the nanoparticle synthesis process, which is generally energy intensive or requires toxic chemical solvents and is costly.